1. Field of the Invention
The present invention relates to apparatus and method for controlling an electromagnetically operable engine valve assembly in which a movable element is driven to move through a control over a current flowing through one of a pair of electromagnets. More particularly, the present invention relates to a technology which enables the use of a technique which corresponds to an increase in resistance due to a viscosity of an engine lubricating oil when a position of the movable element is initialized during an engine start under an engine low temperature region so that a collision between the movable element and the electromagnet can stably be suppressed and a contribution to a reduction in a power consumption can be made.
2. Description of the Related Art
Recently, an adoption of the, so-called, electromagnetically operable engine valves as intake and exhaust valves of an internal combustion engine with an electromagnetic actuator as a power device has been discussed.
In this kind of engine valve, such an initialization control that a movable element rested on a neutral position is moved to an initial position (namely, a position corresponding to a valve closure state) is carried out during an engine start.
To achieve the initialization control, such a technique as to utilize a pendulum motion of a spring-mass oscillation system constituting the spring and movable element and to alternatingly supply a power to a pair of electromagnets disposed on upper and lower parts of the movable element at a timing which is coincident with a specific oscillation frequency of the movable element.
According to the above-described technique, the resonance in the oscillation system is induced, the movable element rested is gradually oscillated widely (an amplitude of the oscillation is gradually increased) so that the movable element can be moved to the initial position.
Japanese Patent Application First Publications No. Heisei 9-195736 published on Jul. 29, 1997 and Heisei 10-288014 published on Oct. 27, 1998 exemplify the initialization control described above.
However, in such a case where the engine is started under the low temperature region (especially, under an extremely low temperature region between xe2x88x9230xc2x0 C. and xe2x88x9220xc2x0 C., a viscosity of the engine lubricating oil in a movable section (including the movable element and its surrounding portion) is increased. To perform the initialization utilizing such a pendulum motion as described in the BACKGROUND OF THE INVENTION (hereinafter, referred to as a resonance initialization), a current value for the one of the electromagnets required to develop the resonance initialization becomes remarkably increased.
As described above, the resonance initialization is not only disadvantageous under the engine low temperature region but also may cause the movable element to be landed onto the one of the pair of electromagnets which is energized to attract the movable element at a high velocity since an electromagnetic force acted upon the movable section becomes excessive when a large current is, at the first time, supplied to the attracted side electromagnet if the resonance initialization is tried to be executed even under the low temperature region. Such a violent collision of the movable element against the corresponding electromagnet is a problem to be avoided from the standpoint of vibration, noise, and durability of the movable element and valve body.
To solve such a problem as described above, a software control technique utilizing a detected position information of the movable element to reduce a landing velocity has been proposed.
According to the proposed software control technique, a highly accurate control of the landing velocity can be achieved by using a model constant (for example, mass, friction, and spring constant) related to the electromagnetically operable engine valve which is a controlled system. Thus, the collision of the movable element against each of the electromagnets can be suppressed.
However, it is difficult to always perform a stable control even if such a software control technique as described above is applied to the electromagnetically operable engine valve. This is because a friction (representing a magnitude of a friction force based on a viscosity of the lubricating oil of the movable section) which is the object of the above-described model constant is largely varied in accordance with a temperature variation and its value is uncertain under the low temperature region.
It is, therefore, an object of the present invention to provide control apparatus and method for the electromagnetically operable engine valve which are capable of executing the initialization control which can stably suppress the collision of the movable element against each or one of the pair of electromagnets and can reduce the power consumption as low as possible under the low temperature region which would make it difficult to execute a favorable resonance initialization due to the increase in the viscosity resistance.
According to one aspect of the present invention, there is provided an electromagnetically operable engine valve assembly for an internal combustion engine, comprising: a movable element; a spring element to bias the movable element at a neutral position; an electromagnet unit faced against the movable element; a control apparatus to control a current supplied to the electromagnet unit to drive the movable element so as to regulate a displacement of a valve body associated with the movable element, the control apparatus comprising: an initialization control section that executes an initialization control such that the current is continuously supplied for the electromagnet unit to move the movable element rested at the neutral position to an initial position; a position detector enabled to detect a position of the movable element with respect to the electromagnet unit; a first current supply control section that performs a feedback control of the current supplied to the electromagnet unit during the execution of the initialization control by a feedback control gain on the basis of the position of the movable element detected by the position detector; and a feedback control gain varying section that varies the feedback control gain in such a manner that as the movable element becomes nearer to the initial position, a velocity of the movable element to arrive at the initial position becomes reduced when the initialization control section executes the initialization control repeatedly until the initialization control has succeeded in moving the movable element to the initial position during an engine start.
According to another aspect of the present invention, there is provided an electromagnetically operable engine valve assembly for an internal combustion engine, comprising: a movable element; a pair of springs to bias the movable element at a neutral position; a pair of electromagnets, each electromagnet being faced against the movable element; a control apparatus to control a current supplied to one of the pair of electromagnets to drive the movable element so as to regulate a displacement of a valve body associated with the movable element, the control apparatus comprising: an initialization control section that executes an initialization control such that the current is continuously supplied to one of the pair of electromagnets to move the movable element rested at the neutral position to an initial position; a position detector enabled to detect a position of the movable element with respect to one of the pair of electromagnets; a first current supply control section that performs a feedback control of the current supplied to one of the pair of electromagnets during the execution of the initialization control by a feedback control gain on the basis of the position of the movable element detected by the position detector; and a feedback control gain switching section that switches the feedback control gain in such a manner that as the movable element becomes nearer to the initial position, a velocity of the movable element to arrive at the initial position becomes reduced when the initialization control section executes the initialization control repeatedly until the initialization control has succeeded in moving the movable element to the initial position during an engine start.
According to still another aspect of the present invention, there is provided a method applicable to an electromagnetically operable engine valve assembly in an internal combustion engine, the electromagnetically operable engine valve assembly comprising: a movable element; a spring element to bias the movable element at a neutral position; an electromagnet unit faced against the movable element; and a control apparatus to control a current supplied to the electromagnet unit to drive the movable element so as to regulate a displacement of a valve body associated with the movable element, and the method comprising: executing an initialization control such that the current is continuously supplied for the electromagnet unit to move the movable element rested at the neutral position to an initial position; detecting a position of the movable element with respect to the electromagnet unit; performing a feedback control of the current supplied to the electromagnet unit during the execution of the initialization control by a feedback control gain on the basis of the detected position of the movable element; and varying the feedback control gain in such a manner that as the movable element becomes nearer to the initial position, a velocity of the movable element to arrive at the initial position becomes reduced when executing the initialization control repeatedly until the initialization control has succeeded in moving the movable element to the initial position during an engine start.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.